The invention relates to a drive unit, particularly for motor vehicles, with a continuously variable cone-pulley transmission, i.e., a transmission that has pairs of conical disks at the input and output sides, respectively, and a chain-belt to transmit torque from one pair of conical disks to the other. The gripping force by which each pair of conical disks holds the chain-belt is applied through belt-tightener control members that are subjected to a pressure which is supplied at least in part by a torque sensor. At least one of the pairs of conical disks has, in addition, a ratio-setting control member. While the belt-tightener control members provide the gripping force, the at least one ratio-setting control member serves to set or change the transmission ratio, i.e., to shift the transmission. The at least one ratio-setting control member receives an amount of pressure that is regulated by a transmission-ratio valve as required to set the ratio that is called for at each point in time. In state-of-the-art arrangements of the kind that the invention relates to, the pressure provided by the transmission-ratio valve can be influenced by a pressure valve that works together with an OR-gate valve. A drive unit of this kind is known from DE 195 46 293 A1.
In the known drive unit of the publication just mentioned, the pressure valve cooperates with the OR-gate valve in such a manner that, if a quick shift of transmission ratios and thus a quick delivery of pressure to the ratio setting servo control member is required and if this pressure delivery cannot be effected to a sufficient extent by the torque sensor because the latter is transmitting only a low level of torque at the particular moment, the pressure valve supplies the transmission-ratio valve with a sufficient level of pressure for a quick position change of the pairs of conical disks and thus a quick shift of transmission ratios. The OR-gate valve in this arrangement receives two different return pressures from the transmission-shifting pressure circuit and automatically takes on a position where only the higher of the two pressures can have an effect on the pressure valve. The OR-gate valve as well as the pressure valve are configured as slide-piston valves and are combined in an arrangement where the respective slide pistons of the OR-gate valve and the pressure valve push against each other.
This known drive unit has an excellent performance record from actual practical use, but a possibility of problems has been recognized in the area of the cooperation between the OR-gate valve and the pressure valve, due to transverse forces occurring at the point where the respective slide pistons of the pressure valve and the OR-gate valve are in contact with each other. The two slide pistons of the known drive unit are arranged in a common cylinder bore hole and push against each other at the place where they are in mutual contact. When a pressure is applied to the slide piston of the OR-gate valve, a normal force in the axial direction of the cylinder bore hole is transferred to the slide piston of the pressure valve. Extended use of the drive unit may cause wear on the valve bore hole, so that the two slide pistons could settle into an angled position in relation to each other. Also, the valve bore receiving the two pistons may already have an initial out-of-straight condition because of production tolerances, which creates another situation where the two slide pistons are not in flush contact against each other.
These problems will have the effect that the force transfer from one valve piston to the other will not be free from transverse forces, so that there is a risk of a valve piston taking on a skewed position inside the valve bore due to the transverse force component. As a natural consequence, the skewed position, in turn, will lead to an increased rate of wear on the valve. Consequently, the condition of the combined system of pressure valve and OR-gate valve can deteriorate to the point where the pressure required by the ratio-shifting valve can no longer be supplied at the prescribed level, so that the desired quick shifting of the ratio of the cone-pulley transmission can no longer be delivered.
It is therefore the object of the present invention to further develop the known drive unit so that a required capability for quick ratio-shifting of the cone-pulley transmission is maintained even after long-term use or in the presence of imperfections in the valve bore.
To meet the foregoing objective, the invention provides a drive unit, particularly for motor vehicles, with a continuously variable cone-pulley transmission, i.e., a transmission that has pairs of conical disks at the input and output sides, respectively, with a chain-belt to transmit torque from one pair of conical disks to the other. The gripping force by which each pair of conical disks holds the chain-belt is applied through belt-tightener control members that are subjected to a pressure which is supplied at least in part by a torque sensor. At least one of the pairs of conical disks has in addition a ratio-shifting control member. While the belt-tightener control members provide the gripping force, the at least one ratio-shifting control member serves to set or change the transmission ratio, i.e., to shift the transmission. The at least one ratio-shifting control member receives an amount of pressure that is regulated by a transmission-ratio valve as required to set the ratio that is called for at each point in time. The pressure provided by the transmission-ratio valve can be influenced by a pressure valve that works together with an OR-gate valve. The force acting between the pressure valve and the OR-gate valve is conducted through an interposed push member which, to a large extent, eliminates transverse force components.
Advantageous embodiments of the invention have, individually or in combination, the features that
the OR-gate valve has a slide piston movable in a valve housing,
the pressure valve has a slide piston movable in a valve housing,
the respective slide pistons of the OR-gate valve and the pressure valve are arranged in a common bore hole of the valve housing.
It is further of advantage if the interposed push member through which the force is transmitted between the slide piston of the OR-gate valve and the slide piston of the pressure valve is at least in part received inside bore holes of the respective slide pistons of the OR-gate valve and the pressure valve in such a way that the push member has freedom of axial movement inside the piston bore holes.
In advantageous embodiments of the invention, the interposed push member is seated in the bore holes of the slide pistons with radial play and axial mobility. Thus, the push member can be moved axially in the slide-piston bores of the OR-gate valve and the pressure valve while the outside circumference of the push member ha s radial clearance from the interior wall of the slide-piston bore. It is advantageous if the radial play is large enough so that the outside circumference of the push member maintains radial clearance from the inside wall of the slide-piston bore in case that the valve bore in which the two slide pistons move does not run true or the two slide pistons are not in alignment with each other. The clearance of the push member inside the slide-piston bore is designed to be wide enough that the outside of the push member will not touch the wall of the slide-piston bore as long as the maximum straightness errors of the valve bore are within the given production tolerance.
According to a further developed embodiment of the invention, the end portions of the interposed push member and the bottom ends of the slide-piston bores are designed as an articulated link connection. The mobility of the link allows the longitudinal axes of the push member, the slide piston of the OR-gate valve, and the slide piston of the pressure valve to position themselves at an angle to each other. The radial play between the push member and the walls of the bore holes in the slide pistons of the OR-gate valve and the pressure valve is wide enough so that even with non-alignment between the interposed push member and the slide pistons of the OR-gate valve and the pressure valve, there is no contact between the outside circumference of the push member and the walls of the bore holes in the respective slide pistons of the OR-gate valve and the pressure valve.
In the arrangement just described, it is advantageous if the end portions of the push member are shaped as spheres or spherical segments and the ends of the slide-piston bore holes are shaped as cones or spherical segments. Thus, when the spherical or spherical segment-shaped ends of the push member are in contact with the conical or spherical segment-shaped ends of the slide-piston bore holes, the contact is a linear contact along a circle, as opposed to a contact between abutting surfaces. Due to the advantageous contacting arrangement, the longitudinal axes of the push member and the slide-piston bore holes of the OR-gate valve and the pressure valve can position themselves at angles to each other as described above.
It has proven to be advantageous if the slide-piston bore hole of the OR-gate valve reaches from the open end of the hole all the way into the opposite axial end portion of the OR-gate slide piston. In the case of the pressure valve, the slide-piston bore hole can extend from an open end to an axial location near a shutter edge of the slide piston of the pressure valve. To add length to the slide-piston bore of the pressure valve, the slide piston can have a tubular lengthwise extension radially surrounding the push member on the outside.
Thus, the invention removes the problem of the slide pistons of the OR-gate valve and the pressure valve being pushed into skewed positions due to the occurrence of transverse forces. When a force is transmitted between the slide pistons, the force is introduced in each of the slide pistons at the deeply recessed end of the respective slide-piston bore, where the longitudinal axes of the interposed push member and the slide pistons are allowed to position themselves at an angle to each other, thereby providing the mobility of a link that reduces the skewing moments acting on the slide pistons as a result of the transverse forces. Thus, if the precise-fitting shape of the valve bore has deteriorated as a result of wear, or if the two slide pistons are not in true alignment, the slide pistons can no longer fall into a twisted or skewed position inside the valve bore due to transverse forces.
The novel features that are considered as characteristic of the invention are set forth in particular in the appended claims. The improved apparatus itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain presently preferred specific embodiments with reference to the accompanying drawing.